US3976031A - Electric discharge coating apparatus - Google Patents

Electric discharge coating apparatus Download PDF

Info

Publication number
US3976031A
US3976031A US05/593,722 US59372275A US3976031A US 3976031 A US3976031 A US 3976031A US 59372275 A US59372275 A US 59372275A US 3976031 A US3976031 A US 3976031A
Authority
US
United States
Prior art keywords
face
substrate
electrode
silent discharge
powder
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US05/593,722
Other languages
English (en)
Inventor
Tsutomu Itoh
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Taiheiyo Cement Corp
Original Assignee
Onoda Cement Co Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Onoda Cement Co Ltd filed Critical Onoda Cement Co Ltd
Application granted granted Critical
Publication of US3976031A publication Critical patent/US3976031A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
    • B05B5/08—Plant for applying liquids or other fluent materials to objects
    • B05B5/087—Arrangements of electrodes, e.g. of charging, shielding, collecting electrodes
    • B05B5/088—Arrangements of electrodes, e.g. of charging, shielding, collecting electrodes for creating electric field curtains
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B14/00—Arrangements for collecting, re-using or eliminating excess spraying material
    • B05B14/40—Arrangements for collecting, re-using or eliminating excess spraying material for use in spray booths
    • B05B14/42—Arrangements for collecting, re-using or eliminating excess spraying material for use in spray booths using electrostatic means
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B14/00—Arrangements for collecting, re-using or eliminating excess spraying material
    • B05B14/40—Arrangements for collecting, re-using or eliminating excess spraying material for use in spray booths
    • B05B14/48—Arrangements for collecting, re-using or eliminating excess spraying material for use in spray booths specially adapted for particulate material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
    • B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
    • B05B5/00—Electrostatic spraying apparatus; Spraying apparatus with means for charging the spray electrically; Apparatus for spraying liquids or other fluent materials by other electric means
    • B05B5/08—Plant for applying liquids or other fluent materials to objects
    • B05B5/081—Plant for applying liquids or other fluent materials to objects specially adapted for treating particulate materials
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working

Definitions

  • This invention relates to an improvement in the electrostatic powder coating apparatus and more specifically to a powder coating apparatus which is characterized by comprising a face-silent discharge electrode capable of generating a silent discharge in the form of a face which is arranged to be separated from and to confront a substrate, means for supplying powder coating material between them, and means for impressing a voltage between the face-silent discharge electrode and the substrate.
  • a powder coating material suspended in the air by means of compressed air is injected against a substrate from a nozzle of a spray gun disposed to be separated from and to confront the substrate.
  • a high DC voltage is impressed on the nozzle of the gun to generate a corona discharge there.
  • the powder in the coating space is charged by virtue of said corona discharge and lines of electric force from the tip of the gun to the substrate.
  • Charged coating material is transferred to a surface of the substrate by a coulomb force caused by the electric field between the tip of the gun and the substrate to form a coating layer of powder material on the surface of the substrate.
  • the resulted layer is baked by heating. This is a usual way to obtain a coating on a substrate.
  • the obtained current has unequivocally a definite value. It is impossible to mutually independently select a value of current and a value of voltage depending on the properties of a powder used. This is responsible for the impossibility of improving properties of the coating.
  • An electrode having a sharp tip is typically employed for generating a corona discharge according to prior electrostatic powder coating systems. A spark due to the corona discharge can run towards the substrate and when a combustible coating material powder is employed, the coating apparatus is in danger of igniting and exploding.
  • One object of this invention is to provide an electrostatic powder coating system which has no drawbacks of the prior electrostatic powder coating systems, enables to obtain an excellent coating having uniform thickness, no pinholes and no surface roughness, and having a remarkably high efficiency.
  • An apparatus according to the system of this invention can be constructed in a small size, can be continuously operated for a long period of time, and is not in danger of being ignited by a spark and exploding.
  • Another object of this invention is to provide a powder coating apparatus which has up to ten times the performance of the apparatus of the prior art.
  • a further object of this invention is to provide an electrostatic powder coating apparatus where a coating material powder not adhered is easily recovered and environmental pollution is thus prevented.
  • the foregoing objects and other objects are achieved by the present invention which comprises an improved electrostatic powder coating apparatus.
  • the apparatus is characterized by comprising a face-silent discharge electrode capable of generating a silent discharge in the form of a face which is arranged to be separated from and to confront a substrate, means for introducing the powder coating material into a coating space between them, and means for impressing a voltage between the face-silent discharge electrode and the substrate.
  • FIG. 1 is a perspective view of a prior art apparatus used for electrostatic powder coating
  • FIG. 2 is a cross-sectional view taken along the planae II in FIG. 1;
  • FIG. 3 is a perspective view, partially cut away, of a face-silent discharge electrode which constitutes a part of the apparatus of this invention, showing the internal structure thereof;
  • FIG. 4a is a schematic illustration, locally showing cross sections, of the first embodiment of the apparatus according to this invention.
  • FIG. 4b is a schematic illustration, locally showing cross sections, of a second embodiment of the apparatus of this invention.
  • FIG. 4c is a schematic illustration, locally showing cross sections, of a third embodiment of the apparatus according to this invention.
  • FIGS. 4d, 4e and 4f are schematic diagrams illustrating the confronting of a face-silent discharge electrode and a surface of a substrate to be coated;
  • FIGS. 5, 6, 7 and 8 are schematic diagrams, partly in cross section, of various face-silent discharge electrodes which pertain to this invention.
  • FIG. 9a is a perspective view of one embodiment of an exhausting-type face-silent discharge electrode employed in this invention.
  • FIG. 9b is a schematic diagram illustrating the construction of the electrode shown in FIG. 9a;
  • FIG. 9c is a schematic diagram illustrating the structure of another electrode
  • FIG. 10 is a perspective view of one embodiment of a blowing-type face-silent discharge electrode employed in this invention.
  • FIG. 11 is a perspective view of another embodiment of a face-silent discharge electrode
  • FIG. 12 is a perspective view of a fourth embodiment of the powder coating apparatus of this invention.
  • FIG. 13a is a perspective view, partly broken away, of a fifth embodiment of the powder coating apparatus of this invention.
  • FIG. 13b is a longitudinal cross section of the embodiment shown in FIG. 13a;
  • FIG. 14 is a perspective view, partly broken away, of a sixth embodiment of the powder coating apparatus according to this invention.
  • FIG. 15 is a perspective view, partly broken away, of a seventh embodiment of the powder coating apparatus according to this invention.
  • FIG. 16 is a perspective view, partly broken away, of an eighth embodiment of the powder coating apparatus of this invention.
  • FIG. 17a is a side view, partially showing sections, of a ninth embodiment of the powder coating apparatus of this invention.
  • FIG. 17b is a traverse cross section of a part of the embodiment shown in FIG. 17a;
  • FIG. 17c is a perspective view of a tenth embodiment of the powder coating apparatus of this invention.
  • FIG. 17d is a side view, partially showing sections, of an eleventh embodiment of the apparatus of this invention.
  • FIG. 18 is a perspective view, partly broken away, of a twelfth embodiment of the apparatus of this invention.
  • FIG. 19a is a perspective view of a thirteenth embodiment of the powder coating apparatus of this invention.
  • FIG. 19b is a longitudinal cross-sectional view of a part of the embodiment shown in FIG. 19a;
  • FIG. 20a is a perspective view, partly broken away, of a fourteenth embodiment of the powder coating apparatus of this invention.
  • FIG. 20b is a longitudinal cross-sectional view of a part of the embodiment shown in FIG. 20a.
  • a spray gun is denoted by the reference numeral 190, a compressed air source by the reference numeral 191, a storage bin for powder coating material by the reference numeral 192, a power source by the reference numeral 193, a powder coating material by the reference numeral 194, tips of the gun by the reference numerals 195, 195-1, 195-2 and 195-3, a substrate by the reference numeral 196, an electric wire by the reference numeral 197, and a coating by the reference numeral 199.
  • Back ionization occurs at location 205.
  • the distribution of electric current is denoted by a curve identified by reference numeral 206.
  • an imaginary plane II is depicted for locating the cross section in FIG. 2.
  • a face-silent discharge electrode 2 is disposed generally parallel in front of a substrate 10, both being separated by a space 18.
  • the substrate 10 is a plane board.
  • a powdery coating material 11 is allowed to pass in small amounts from a feeder of coating material to a duct 15 and is suspended in a conveying air which is circulated in a closed circuit composed of a duct 15, a duct-recovering opening 16, a duct 13 and a duct 14 by means of a fan 17. The suspended coating material is thus fed to a coating space 18.
  • the face-silent discharge electrode 2 which embodies an essential feature of this invention has the mechanical structure as shown by FIG. 3.
  • two alternate groups of parallel electrode bars 1--1 and 1--2 are arranged at equal distances beneath but near the surface of an insulator 2.
  • a group of every other bar is connected in common to a terminal and the other group to another terminal.
  • a high alternating voltage is impressed between said terminals by means of an alternating current source 6 (FIG. 4a).
  • alternating lines of electric force 3 in a form convex to the outside of the face-silent discharge electrode appear between electrode bars 1-1 and 1-2.
  • the distribution of the density of the current which is carried by coating material powder particles and ions both entering the surface of the substrate is uniform in a high degree, because lines of electric force in the coating space 18 which are directed from the face-silent discharge electrode to the substrate 10 forms a uniform field.
  • a coating 19 having a high degree of evenness is formed on the surface of substrate 10 within some seconds.
  • the conspicuous effectiveness can be sufficiently appreciated in many cases where the space including coating material powder is enclosed with a face-silent discharge electrode or electrodes and a substrate as is shown by FIG. 4d, 4e or 4f. These figures illustrate the way that a face-silent discharge electrode is separately disposed in front of a substrate.
  • FIG. 4d The way, detailed in the explanation above for FIG. 4a, that a face-silent discharge electrode is arranged separately in front of a substrate is shown in FIG. 4d.
  • the powder coating apparatus therein is constructed so that a dispersed powder is introduced perpendicularly towards the back of the sheet as shown by arrows 15' in the space 18 which is between a substrate 10 and a face-silent discharge electrode 3 separated from and confronting the former.
  • guard rings 36-1 and 36-2 can be arranged.
  • enclosing the coating space 18 principally with a face-silent discharge electrode 2 and a substrate 10 is one feature of this invention for arranging the substrate separated from and confronting the face-silent discharge electrode.
  • FIG. 4e A second representative embodiment for arranging the substrate separated from and confronting the face-silent discharge electrode in accordance with this invention is shown in FIG. 4e.
  • the space 18 in which a coating material powder exists is enclosed with the surface of a silent discharge electrode 2 and a substrate 10 almost the entire surface of which is surrounded by the face-silent discharge electrode.
  • An interstice 300 may be made in a part of the face-silent discharge electrode 2 for disposing a device 9 which introduces and supports a substrate 10 in a predetermined position, and connects it to ground. Such interstice, however, does not interfere with the operation of this invention.
  • FIG. 4e arrows 15' show the direction of flow of coating material powder in a coating chamber 18 perpendicularly into the plane of the drawing sheet.
  • the details of connecting every electrode bar 1-1 or 1-2 with an AC source is omitted, as in FIG. 4d.
  • FIG. 4f illustrates the third representative embodiment of arranging the substrate separated from and confronting the face-silent discharge electrode in accordance with this invention.
  • the surface to be coated is the inner surface of a substate 10.
  • the apparatus is composed so that the substrate 10 may encompass a coating space 18 where a coating material powder introduced as shown by arrows 15' is suspended.
  • a face-silent discharge electrode 2 Inside the substrate is disposed a face-silent discharge electrode 2 the surface of which confronts the inner surface of the substrate with interposing a coating space 18 containing coating material powder.
  • a passage 300 may be made in a part of the substrate so that the face-silent discharge electrode may be mechanically supported and provided with necessary AC and DC voltages. The existence of said passage should be considered to have no relation to the essential feature of this invention.
  • FIG. 4f Although detailed connection of an AC power source 6, a DC power source 7 and a conductor 8 of the face-silent discharge electrode and an earthing conductor 9 for the substrate 10 are omitted in FIG. 4f, all of them are the same as in the explanation mentioned above.
  • the embodiments of arranging a face-silent discharge electrode separated from and confronting a surface to be coated of a substrate according to this invention can be summarized as an essential feature that a space including a coating material powder is enclosed with a face-silent discharge electrode and a surface to be coated.
  • the great advantage in the embodiment of disposing a surface to be coated of a substrate separated from and confronting a face-silent discharge electrode of the apparatus of this invention is based on that the form of said face-silent discharge electrode can be shaped, depending upon the shape of a substrate.
  • the shape of face-silent discharge electrode may be modified so that both the surface density of lines of electric force, terminating at the surface of the substrate, in said surface of substrate and the density of the current flowing into the surface to be coated of the substrate may be generally uniform.
  • a mere plane face-silent discharge electrode separated from and confronting the substrate cannot give a uniform surface density of lines of electric force and a uniform current density in the surface to be coated of substrate 10, i.e., the inner surface of substrate 10.
  • a face-silent discharge electrode 2 having a U-shaped section is arranged so as to maintain a nearly equal distance from the surface of the substrate to be coated.
  • the powder which has been introduced as denoted by arrows 15'-1 and 15'-2 can form a powder layer excellent in evenness on the inner side of U-shaped substrate 10 within a short period of time.
  • guard rings 36-1 and 36-2 may be disposed to regulate the disturbance of the electric field at the end parts of the substrate, if necessary.
  • the inner sides of the guard rings directly face the coating space 18 and can be face-silent discharge electrodes or curtains for an electric field, if desired.
  • power sources 36-16 and 36-26 as well as conductors 36-19 and 36-29 can be employed.
  • FIG. 4c a detailed wiring diagram for electrode bars 1-1 and 1-2 disposed near beneath the surface of face-silent discharge electrodes is omitted. As detailed above in connection with FIG.
  • the shape of the face-silent discharge electrode to be disposed separated from and confronting the surface of substrate can be modified so that both the surface density of lines of electric field, terminating at the surface of substrate, and the current density in the surface of substrate is uniform.
  • the forming of a coating of even thickness on the substrate as a result of the above construction constitutes an advantageous feature of this invention.
  • the ionic current density into the surface of the substrate can be maintained at a definite value
  • another advantageous fature of this invention is that the current density can be changed.
  • the thickness of the resultant powder layer on the substrate can be controlled, as desired.
  • a very long substrate 10 extends vertically from a feed opening 15 of powder coating material to an over spray-recovering opening 16.
  • the coating is practiced with a face-silent discharge electrode generating a uniform intensity of silent discharge on the surface along its entire length caused by impressing the same AC voltage from a power source 6 as shown in FIG. 4a, then the powder layer 19 formed on the substrate 10 usually in thickest near the feed opening 15 for a powdery coating material, a little thinner in the intermediate position, and thinnest near the over spray-recovering opening 16.
  • this tendency to form an uneven layer is conspicuously lower as compared with results from prior art spray guns.
  • the coating unevenness is not adequate when a uniformly thick layer is desired.
  • This problem can be solved by dividing the electrode bars beneath and near the surface of the face-silent discharge electrode 2 into, for example, three groups and impressing an AC voltage having a different peak value on each of groups by means of AC sources 6-1, 6-2 and 6-3, as shown in FIG. 4b.
  • a sufficiently strong current is initially allowed to flow through parallel electrode bars in area A by an impression of a high voltage.
  • the electrode bars in areas B and C also are impressed with the same voltage as that in area A.
  • the voltage of source 6-1 for impressing voltage on electrode bars in area A is regulated to a lower level after a certain period of time.
  • the voltage of source 6-2 for impressing an AC voltage on electrode bars in area B is lowered.
  • the high AC voltage impressed on electrode bars in area C is maintained to the last by the source 6-3.
  • the discharge current density can be controlled depending upon the time and the locality on the substrate and it is possible to control the thickness of a coating on a substrate as desired.
  • an excellent coating having a uniform thickness and no pinholes is obtained by modifying the shape of face-silent discharge electrode, or by dividing the face-silent discharge electrode into areas and impressing a controlled DC voltage and/or a controlled AC voltage, depending upon the time and the locality, independently on each of the divided areas. Moreover, a combination of modifying the discharge electrode and impressing a controlled voltage can bring an excellent even layer of powder on substrates of more complicated shapes.
  • the first characteristic of the powder coating apparatus according to this invention consists in that the evenness in thickness of the coating obtained is very good and the coating has an extremely low surface roughness and no more than a few pinholes.
  • This is due to the facts that the electric field in the coating space 18 of powder coating apparatus of this invention is approximately homogeneous and the density of current which flows into the substrate 10 is nearly homogeneous, as elucidated by the explanation of FIG. 4a.
  • the generation of pinholes and surface roughness due to back ionizing phenomenon caused by non-uniformity of current density is prevented, and a powder layer even in thickness is obtained, as opposed to that obtained in prior apparatus as shown in FIG. 2.
  • the second characteristic of the powder coating apparatus of this invention consists in that the thickness of the coating to be obtained can be easily controlled.
  • a current density flowing the coating space 18 and a field strength in the coating space 18 can be mutually independently adjusted by controlling mutually independently an AC source 6 and a DC source 7. Accordingly, a thickness of a powder layer to be obtained can be changed within a broad range as required by the properties of the powder employed. For example, in the case of the powder having a relatively high electric resistivity, an extremely thick coating may be obtained by limiting the current to a low value and applying a high field strength. A thin coating may be obtained by flowing a relatively strong current and applying a relatively weak field. The control of thickness can be easily performed as mentioned above.
  • the third characteristic of the powder coating apparatus of this invention consists in that the coating efficiency markedly increases.
  • charging powder particles in the coating space 18 can be performed at a high efficienty, because a powder in a well dispersed state is fed into the coating space 18.
  • the field strength can be increased to a high value, as compared with that in a prior electrostatic powder coating apparatus, because the field strength in the coating space is uniform.
  • the efficiency of charging powder particles is high and the field strength is high, adhering of powder coating material to the substrate is performed markedly efficiently, and the efficiency of adhering may be close to 100% in almost all cases.
  • the fifth characteristic of the apparatus according to this invention consists in that the size of said apparatus is markedly small. This is due to the fact that a suspension of coating material powder which has been preliminarily dispersed in a gas may be distributed over the surface of the electrode and powder particles are driven into the coating space from everywhere above the surface. Thus, it is unnecessary to force the coating material powder to disperse during the flight of powder blown from a gun to a substrate, such as is the case with prior spray guns. Accordingly, the face-silent discharge electrode can be disposed very close to the substrate. Usually, a distance of 5-20 cm from a substrate is sufficient. In an extreme case, disposing the electrode within one centimeter from the substrate is possible. Moreover, a remarkably high field strength is obtainable, because the electric field in the coating space 18 is nearly uniform. These factors enable the size of the apparatus to be remarkably decreased. Additionally, the apparatus of this invention requires no booth construction.
  • the sixth characteristic of this invention consists in that the performance of the apparatus is very good.
  • the discharge electrode can be arranged very near to the substrate, and the field strength between them can be very high. Accordingly, the velocity of flight of powder particles to the substrate is very high.
  • powder particles are fed from everywhere. Hence, the entire surface of substrate can be coated all at once without any motion of a spray gun.
  • the powder coating apparatus of this invention can easily have to ten times the performance of prior powder coating apparatus, even though the former has a fraction of the size of the latter.
  • the seventh characteristic of the powder coating apparatus of this invention consists in that a continuous automatic operation for a very long time is practicable without any maintenance service. This is mainly due to the fact that powder particles cannot adhere to the face-silent discharge electrode by virtue of a repulsion force to powder particles with which said discharge electrode is essentially provided.
  • alternating lines of electric force 3 between electrode bars adjacent each other which are convex to the outside cover the entire surface of the face-silent discharge electrode according to this invention.
  • a charged powder particle in the area near the surface oscillates along a line of electric force convex to the outside.
  • said particle is always subject to a centrifugal repulsion away from the electrode surface. For this reason, no powder particles in the coating space adhere to the surface of a face-silent discharge electrode.
  • the eighth characteristic of the powder coating apparatus of this invention consists in that said apparatus is remarkably safe.
  • the discharge energy generated is distributed on the entire surface of an electrode, no fire can be caused by electric discharge.
  • the electric field concentrates at a point, i.e., a tip of spray gun in a prior electrostatic coating apparatus employing corona discharge.
  • the tip of spray gun is usually connected to a power source via a high resistance.
  • high resistances 51 and 52 may be inserted for further safety.
  • Conductor electrodes of a powder coating apparatus of this invention can be made to have no exposed surface.
  • the powder coating apparatus of the present invention has a very high safety as compared with apparatus of the prior art.
  • this invention can be said to have a feature, in an aspect, that the apparatus is devised according to a novel technical idea entirely different from the prior electrostatic powder coating apparatus employing a so-called spray gun and booth.
  • the powder coating apparatus of the present invention cannot be divided into a spray gun part and a booth part according to the concept of the prior art.
  • an efficiency of adhering as high as 95% or more is usually attained in a discharge space by the method of this invention.
  • the apparatus can be constructed so as to automatically recover powder particles not adhered in the system. And the recovered particles as such can be employed again. Thus, there is no generation of a so-called over spray.
  • the recovering device in itself can be said to be a spray gun in the case of the apparatus according to this invention. Therefore, the apparatus of this invention has an epoch-making performance in that powder coating is always performed with an efficiency of almost 100% and no environmental pollution is created.
  • FIG. 4a where a face-silent discharge electrode is generally board-shaped and a coating material powder suspended in a gas is fed from a peripheral part is no more than one embodiment of this invention.
  • the apparatus can be constructed as illustrated by FIG. 11 where the face-silent discharge electrode is divided into three parts 29, 30 and 31 and they are separated from each other by slits 29-30 and 30-31.
  • Some parallel electrode bars 1-1 and 1-2 are horizontally buried beneath and near the surfaces of three face-silent discharge electrodes 29, 30 and 31.
  • a high AC voltage from an AC source 6 is impressed thereon to generate a stable silent discharge over the entire surfaces of electrodes 29, 30 and 31.
  • the DC power source 7 and the conductor 8 supply a potential between the face-silent discharge electrode and a substrate not shown.
  • the high DC voltage to be impressed from the DC source is not necessary to have a definite value.
  • a high pulsed voltage may preferably be used in some cases.
  • FIG. 9a there is shown a perspective view of one embodiment of exhausting-type face-silent discharge electrode employable in this invention.
  • electrode bars 1-1 and 1-2 which have been disposed parallel and at equal distances are separately coated with an insulator or a semi-conductor and all electrode bars adjacent each other are connected to one side of the source 6.
  • a filter cloth 23 is positioned behind the array of electrode bars.
  • a porous plate 27 is arranged behind cloth 23.
  • FIG. 9c The sectional view of the structure of the electrode is shown in FIG. 9c. All these parts are fixed to a hood 21 to which a duct 24 is connected. An AC voltage is impressed between the electrode bars 1-1 disposed in the front end part of the hood and the porous plate 27 disposed behind the filter cloth 23.
  • a silent discharge is generated between the electrode bars 1-1 and the porous plate 27.
  • a silent electric discharge is generated in the space in the form of a layer between the face including parallel electrode bars and back-up porous plate 27.
  • the face-silent discharge electrode of the type shown is for exhausting only the air from the coating space to flow out of the system through a duct 8, as shown by arrow 24, and for causing the powder particles in the coating space 18 to adhere to the substrate.
  • the powder particles which have been charged in virtue of a field ionic current present between the face-silent discharge electrode and a substrate flow countercurrently to air 25 being exhausted.
  • only gas can be exhausted through the filter cloth 23 and powder particles are attracted by the substrate to counterflow at a speed of up to some ten times the speed of said gas.
  • This type of exhausting face silent discharge electrode will be explained hereinafter in an example.
  • FIG. 9b Another example of the exhausting-type face-silent discharge electrode is demonstrated in FIG. 9b.
  • An AC voltage is impressed between two adjacent electrode bars 1-1 and 1-2 both coated with an insulator or a semi-conductor and a silent discharge is produced between them.
  • Ions generated by means of a DC power source 7 are introduced into the coating space 18.
  • alternate parallel electrode bars 1-1 and 1-2 both coated with an insulator or a semi-conductor are connected in common and are fixed to a hood 21 as shown.
  • a mixture of air and a coating material powder is blown in from a duct, shown by arrow 22, against a substrate through spaces between parallel electrode bars 1-1 and 1-2, as shown by arrows 28.
  • This is a blowing-type face-silent discharge electrode for the coating operation.
  • the voltage is applied in the same manner as in FIG. 9a.
  • insulator or semi-conductor for insulating adjacent electrode bars.
  • Such insulator or semi-conductor forms integral parts of a board, or coats the individual electrode bars separately.
  • the combination of such a board and individually coated electrode bars can also be employed.
  • the resistivity of the insulator or the semi-conductor employed can be selected from a wide range.
  • the value of electric resistance of insulator or semi-conductor to be employed is desired not to be high.
  • a value in the range of 10 8 -10 14 ⁇ cm must be selected in consideration of the service conditions.
  • Employable materials include organic insulators, such as epoxy resins, fluorine plastics and vinyl chloride resins; modified resins thereof having a somewhat lowered resistivity; inorganic insulators or semi-conductors, such as glass, boron nitride, porcelain, cement and asbestos.
  • organic insulators such as epoxy resins, fluorine plastics and vinyl chloride resins
  • modified resins thereof having a somewhat lowered resistivity such as glass, boron nitride, porcelain, cement and asbestos.
  • the frequency of AC voltage employed in this invention of 10-200 Hz is preferred when the effect of preventing powder-adherence to the electrode is desired. Otherwise, a value to be selected need not be limited to said range.
  • feeding powder preliminarily suspended in air into the coating space is referred to as the method of feeding powder.
  • the use of air as dispersion medium is not a necessary condition for feeding a coating material powder dispersed in a gaseous medium. Any suitable gas can be selected, depending, of course, upon the properties of powder used or the like.
  • One method for feeding a coating material powder into the coating space is an electrodynamical method.
  • powder particles fed through ducts or troughs may be preliminarily charged and may be fed to the coating space through an electric field, such as a non-uniform travelling wave alternating electric field and a non-uniform standing wave electric field, by the aid of the gravitational force or a conveying gas.
  • an electrodynamic method e.g. using an electric field curtain device, may be also employed for recovering powder not adhered.
  • FIG. 12 illustrates an example therefor.
  • Electrode bars are embedded beneath and near the inner surface of a hopper 42 Electrode bars are connected in common every third bar and a three-phase alternating electric field from source 50 is impressed on them to generate a non-uniform travelling wave alternating electric field. Powder particles not adhered to said inner surfaces are immediately excluded through a gate 43.
  • the powder coating apparatus shown in FIG. 12 is meticulously constructed so as to give a volume density of coating material powder as uniform as possible in the coating space.
  • a coating material powder is fed from powder feed openings 37-1, 37-2, 37-3, 38-1, 38-2 and 38-3 sideways to the lines of electric force which passes from the face-silent discharge electrode to the substrate. Gas is prevented to be entrained by powder particles by means of an electrodynamical force.
  • a coating material powder is fed by an electrodynamical method from powder feed openings 39-1, 39-2 and 39-3 which is provided with the face-silent discharge electrode 39 itself.
  • FIGS. 13a and 13b there is shown a detailed illustration of an embodiment of this invention where the inner surface of a pipe-shaped article 10 is powder coated.
  • Substrate 10 is a pipe having a rectangular section.
  • a face-silent discharge electrode 2 having a rectangular section is suspended into said rectangular pipe so as to retain a certain distance between the outer surface of the electrode and the inner surface of the pipe.
  • the face-silent discharge electrode is fixed to the lower end of a duct 45 for powder feeding by a fitting 47 to compose a delivery slit 49.
  • Duct 45 provides powder feeding and, together with said face-silent discharge electrode, is suspended by a retainer (not shown) to maintain a certain distance to the inner wall of the substrate 10.
  • the surface-silent discharge generating electrode is an electrode having a structure such as illustrated in FIG. 4a.
  • an AC voltage is applied thereto by means of a power source 6.
  • a power source 7 is connected to the face-silent discharge electrode via conductors 44.
  • Dispersed powder fed between the face-silent discharge electrode and the substrate 10 through duct 45 as shown by arrow 46 is immediately charged by an ionic current of the same polarity which flows from the face-silent discharge electrode to the substrate 10. By virtue of the electric field between them, a uniformly thick layer of powder is formed on the inner surface of the substrate 10.
  • an inner surface of an elongated pipe-shaped article can be powder coated with a very simple apparatus with a high efficiency, in accordance with this invention.
  • a substrate and a coating apparatus are sustained upright as illustrated above. Even if a substrate and a coating apparatus are sustained in oblique or horizontal positions, the powder coating can be performed provided, of course, that powder dispersed in a gas is fed in a coating space or a powder is conveyed into a coating space by an electrodynamic method, such as by a conveying device of an electric field curtain.
  • an electrodynamic method such as by a conveying device of an electric field curtain.
  • the face-silent discharge electrode can be considerably elongated, if necessary, in the apparatus of this system for coating the inner surface of pipe-shaped substrate, a powder which has been introduced into the coating space through the slit 49 can adhere perfectly to the inner surface of said substrate in a 100% coating efficiency.
  • a powder layer having depths different in the longitudinal direction of the substrate may be easily obtained.
  • a rectangular duct 53 surrounds a substrate 10 which is continuously moving along the direction denoted by arrow 70.
  • Many injecting openings 56 are arranged on the sides of the duct.
  • a powder coating material conveyed by a gas shown by arrow 55 enters the rectangular duct 53 at a port 54 and is injected from injecting openings 56 upstream to a recovering rectangular duct 57 and downstream to a recovering rectangular duct 61.
  • the side confronting the injecting openings 56 of the upstream recovering rectangular duct 57 is provided with many recovering openings 58 as shown in the figure.
  • the mixture of a conveying gas and a coating material powder which has been injected from injecting openings 56 directed downstream runs towards the downstream recovering rectangular duct 61.
  • the side confronting the injecting openings 56 of the downstream recovering rectangular duct 61 is provided with many recovering openings not shown. Through them, the gas for conveying the coating material powder is recovered and is excluded from an exit opening 62 out of the system as shown by arrow 63.
  • the rectangular duct 53 for injecting coating material, said upstream recovering rectangular duct 57 and said downstream recovering rectangular duct 61 are connected with two face-silent discharge electrodes 2-US and 2-DS to compose a unit surrounding a substrate 10. Both the upstream electrode 2-US and the downstream electrode 2-DS are of rectangular cylindrical form. In the inner sides of these are arranged many parallel electrode bars denoted by the reference numeral 1.
  • An AC voltage is impressed between the adjacent electrode bars 1 by means of a power source 6. Moreover, a DC voltage is impressed on them by a power source 7 grounded via conductor 8 to generate a high potential difference to substrate 10 grounded via conductor 9.
  • electrode bars in the surface of the face-silent discharge electrode confronting the bottom surface of the substrate 10 are connected to every third bar and a three-phase alternating voltage from the power source 65 is impressed thereon to generate a non-uniform travelling wave alternating electric field on the surface. Accordingly, face-silent discharge electrodes 64-US and 64-DS convey a minute amount of particles which have fallen to slits 66-US and 66-DS to collect. These particles can be easily recovered from excluding openings 68-US and 68-Ds.
  • the face-silent discharge electrode functions as a recovering device in collecting powder particles not adhered, if any, together with feeding an ionic current for coating and forming an electric field for adhering, in this case.
  • the apparatus of this invention can be constructed so as to exclude no coating material powder from these gaps, because ambient air is allowed to enter the apparatus through these gaps and can be exhausted from the exit openings 61 and 62 together with the conveying gas as shown by arrows 60 and 63.
  • a powder coating apparatus for continuously coating a single side of a substrate of continuously fed sheet and a method for controlling the powder layer formed is now described.
  • parallel electrode bars 1 are disposed in the inner side of a face-silent discharge electrode 2 which is disposed to be separated from and to confront a surface of a substrate 10 proceeding continuously in the direction shown by arrow 70.
  • An AC voltage from an AC source 6 is impressed between them to generate a silent discharge.
  • Positive or negative ions produced by said discharge are stably fed to an upper surface of the substrate 10 by virtue of a DC voltage impressed from a DC power source 7.
  • a powder coating material 81 which has been injected towards the upper surface of the substrate from injecting opening 80 electrostatically, rapidly adheres to the surface of the substrate 10 to form a powder layer having an even thickness.
  • the bulk powder coating material 11 is fed to a coating material powder-fluidizing chamber 77 by means of a coating material feeder 12.
  • the floor of said coating material powder-fluidizing chamber is composed of a perforated board 78 which in turn is the ceiling of a blowing chamber 76.
  • a fludizing coating material powder 79 is always present in the lower part of the coating material powder fluidizing chamber 77.
  • the powder which has been dispersed to a suitable extent by the air 77 is stably injected from the injecting opening 80.
  • the process can be devised so that a large quantity of powder particles not adhered does not remain in the gas exhaust through the duct 83.
  • the electric resistance of powder coating material varies in a markedly wide range, depending on the humidity of the gas, and the properties of the powder itself vary in a wide range, it may be enormous in many cases that the face-silent discharge electrode is made to be sufficiently long, in the direction shown by arrow 70, for all these cases. Accordingly, the length of the electrode is adequately determined and the operating conditions of the silent discharge generating electrode 2 are adjusted thereto.
  • the size of the apparatus is reduced and a control of the quality of the resulted coating material powder layer is performed, a satisfactory utility will be obtained in many cases from the viewpoint of the practice.
  • FIG. 15 An automatic control system for such control of quality is also illustrated in FIG. 15. Powder particles not adhered which are contained in the exhaust duct 83 is detected by a powder concentration detector 84 and the output signal thereof is fed back to a voltage controlling device 6c for an AC source 6 and to a 6c controlling device 7c for a DC source 7. As the intensity of a silent discharge generated on the surface of a silent diacharge electrode is dependent upon the humidity in a gas, said humidity may be detected by means of a current transformer 6-DC and the output signal therefrom also may be fed to an AC voltage-controlling device 6C.
  • a control of the value of DC current is performed with a direct current-detecting resistance 9D and a direct current-controlling device 9-DB.
  • the DC and AC voltages may be automatically controlled by the outputs from an alternating silent discharge current detector 6-CB and said direct current-controlling device 9-DB, respectively. Manual controls of the operation may be effectively performed by viewing indicators attached to these detectors.
  • the apparatus shown is used for coating an outer surface of a separate body, such as a utensil or a case for an electrical appliance in accordance with this invention.
  • Baffles 91-U and 91L having rectangular pipe-formed slits 92-U and 92-L positioned in horizontal planes are arranged over and under face-silent discharge electrodes 2, 2-R1 and 2-R2, respectively.
  • the electrodes are combined in the form of an upright rectangular pipe.
  • Over and under the baffles are positioned an upper hood and duct 94 and a lower hood and duct 91, respectively.
  • a high AC voltage from a power source 6 is impressed on face-silent discharge electrodes 2, 2-R1 and 2-R2, to provide a face ion source. Simultaneously, a high DC voltage is impressed thereon by a power source 7 and a conductor 8.
  • a substrate 10 to be coated is suspended by a conveyor line 90 which is grounded via a conductor 9.
  • the face ion source 2-R1 is vertically movable as shown by arrow 2-RD and forms a door. As the substrate is forwarded, the door is lowered. Then, the substrate 10 is set in the position corresponding to the center of face-silent discharge electrodes 2, 2-R1 and 2-R2. Thereafter, the ion source 2-R1 is closed. The surface of the substrate 10 to be coated is thus surrounded with face ion sources on all sides.
  • a powder coating material suspended in a gas is introduced upwardly into the apparatus, as shown by arrow 93.
  • the mixture of powder coating material and gas moves upward, being directed by slits 92-L and 92-U, in a space between face ion sources and the substrate, meanwhile a silent discharge is generated on the surfaces of face ion sources and a high DC voltage is impressed between said face ion sources and the substrate by a power source 7.
  • the upward moving powder coating material immediately forms a powder layer uniform in thickness on the surface of the substrate 10.
  • the face-silent discharge electrodes may be divided in several sections in the vertical direction, as illustrated in FIG. 4b.
  • the voltages impressed on them as well as the timing of impression may be controlleld to obtain a coating having desired distribution of thickness on the substrate.
  • the coating efficiency may attain to 95% or more.
  • the face-silent discharge electrodes in FIG. 16 are planar, said electrodes within the scope of this invention can have suitable curved surfaces for coating outer surfaces of separate bodies.
  • curved surfaces of the electrodes By virtue of curved surfaces of the electrodes, a uniformly thick coating will be formed even on surfaces of a body having an extremely complicated shape in a short time.
  • the face ion sources surrounding a substrate may be divided into parts and different AC voltages may be impressed on said parts depending upon both the shape of substrate and required thicknesses of the coatings.
  • objects such as the increase of efficiency of the apparatus, reduction in size of apparatus and prevention of generating coating material over-spray, can be effectively achieved by employing, as face-silent discharge electrodes, exhausting types or blowing types which are illustrated in FIG. 9a, 9b, 9c, 10 and 11, not to mention the plane-silent discharge electrode.
  • a body 10-1 is a substrate the entire surface of which is required to be powder coated and is suspended by a conveyor line 90 earthed via a conductor 9 and is being introduced to a coating apparatus of this invention.
  • a body 10-2 is a finished substrate.
  • a door 127 of which the inner side constitute a face-silent discharge electrode is opened and the substrate 10-1 is continuously introduced into the coating apparatus.
  • two of four sides of the coating chamber, which are perpendicular to the direction of moving conveyor are composed of a face-silent discharge electrode 128 and a door 129 and a face-silent discharge electrode 129 and a door 127.
  • the ceiling of the chamber is composed of a face-silent discharge electrode 142 and the floor is composed of a bottom face-silent discharge electrode not shown.
  • the sides 120-1 and 120-2 which are parallel to the direction of the conveyor line 90 are composed of face-silent discharge electrodes of the exhausting type as shown by FIG. 9a.
  • a small quantity of ambient air is introduced through interstices between doors and frames and slits for allowing hangers which support substrates. Due to this exhausting, the coating material powder is prohibited from passing out of the apparatus.
  • the coating material powder is fed from coating material-injecting devices 135 and 136 which are disposed at the four corners of the chamber.
  • air 140 is blown in and carries the powder coating material fed as shown by arrow 138 at a high speed through a duct 139 to feed the injecting device 135.
  • the injecting device 135 feeds the coating chamber with a coating material powder suspended in air, through an injecting opening 137 of each injecting device. As both lines of electric force and ion currents flow to the substrate in the chamber from all directions, all surfaces of the substrate can be coated within some seconds.
  • the coating material-carrying air and the air from interstices of the chamber are exhausted as shown by arrows 131 and 134, the coating material powder is attracted by the substrate irrespective of the flowing direction of air.
  • This effect is given by the use of face-silent discharge electrodes as shown in FIG. 9a.
  • No coating material powder passes out of the chamber and a powder coating of separate bodies is performed safely and rapidly.
  • the floor of the apparatus is composed of a face ion source capable of transferring powder due to a travelling wave-type electric field, a minute quantity of powder particles not adhered can be excluded from the apparatus, if necessary, as shown by arrow 141.
  • a high AC voltage is impressed on every face-silent discharge generating electrodes by means of an AC power source and a high DC voltage is concurrently impressed on the same, as in other cases.
  • Face-silent discharge electrodes 120-1 and 120-2 include parallel electrode bars 121 which are arranged at suitable distances, coated with an insulation and disposed in the inner surface part of the electrode.
  • a filter cloth is extended downstream.
  • a backup plate is disposed further downstream. Behind backup plate is a hood 124 to form a blowing chamber 123.
  • the electrode is constructed so that the air may be exhausted from a duct 134 as shown by arrow 132.
  • the powder coating apparatus coats all the surfaces of the substrate which is surrounded by a plurality face-silent discharge electrodes.
  • the coating can be practiced by rotating a substrate, by selecting the positions of the coating material feeding openings, or by selecting the directions in which a coating material is blown in, without all the surfaces to be coated being surrounded by face-silent discharge electrodes.
  • a plurality of substrates 10 are introduced successively into a coating apparatus through an opening 152-1 by means of a conveyor line 90 which is grounded via a conductor 9.
  • Completed substrates exit one by one through an exit 152-2.
  • the inner surface of sides 150 and 151 are composed of face-silent discharge electrodes according to this invention.
  • the inner surface parts adjacent to the exit 152-2 of the coating apparatus are composed of face-silent discharge electrodes 160 and 167 of exhausting type.
  • the inner surface part 153 at the entrance of the apparatus and the inner surface part 154 at the exit are composed of face-silent discharge electrodes.
  • the ceiling is also composed of face-silent discharge electrodes and includes a slit 157 for passage of hangers 158 which support the substrates.
  • the floor 168 of the apparatus is composed of a face-silent discharge electrode of the travelling wave type.
  • a high AC voltage from a power source 6 is impressed on the inner surface parts 150, 151, 153 and 154, the inner surface parts of the electrodes 160 and 163, and the surface parts confronting the slit 157.
  • a DC voltage from a power source 7 and a conductor 8 is impressed on every inner surface part so as to generate a DC electric field between the substrates 10 and said inner surface parts.
  • a three-phase alternating voltage is impressed on the inner surface part of the floor 168 by a power source not shown to generate a silent discharge of the travelling wave type.
  • the air in the apparatus flows generally in the direction from the entrance to the exit. Only air which has lost almost all suspended powder particles is exhausted through face-silent discharge electrodes 160 and 163 of the exhausting type as shown by arrows 162 and 165. A minute quantity of powder particles not adhered, if any, is automatically recovered as shown by arrow 169 by means of the silent discharge electrode 168 which constitutes the floor of the apparatus.
  • the substrates 10 can be continuously powder coated by employing silent discharge electrodes in the form of simple plane in accordance with the apparatus of this invention.
  • the coating of various kinds of articles is desired.
  • the powder coating can be easily achieved by dividing the face-silent dischage electrode into parts and impressing a different AC voltage and a different DC voltage on each of said parts, or by merely regulating the DC voltage.
  • the substrate has a highly different shape or dimension, the following techniques are used. If the diameters of substrates are far different, the breadth of the apparatus should be regulated as shown by the reference numeral 167.
  • the length of the part of the apparatus shown by an imaginary line 166 is varied.
  • a coating of good quality will be obtained at a high efficiency by adjusting the shape of the face-silent discharge electrodes disposed to be separated from and to confront the substrate.
  • the provision of face-silent discharge electrodes of various dimensions and/or shapes corresponding to substrates of various dimensions and/or shapes thus enables the apparatus to powder coat various substrates.
  • the apparatus of the present invention is not limited to a conveyor system with a high DC voltage impressed on face-silent discharge electrodes.
  • the powder coating can be practiced even when a high DC voltage is impressed on the substrate 10 via a contacting device installed on the conveyor line or when the hangers are insulated from conveyor line. Whether the coating is performed with positive ions, or with negative ions depends upon the electrification characteristics of a coating material powder. Thus, both kinds of ion current are employable.
  • the coating material powder is suspended in a gas introduced between the substrate and face-silent discharge electrodes confronting the substrate, irrespective of the method for conveying employed, i.e. conveying by a gas flow or conveying by an electrodynamical force.
  • powder coating can be carried out even when a coating material powder is fed to a face-silent discharge electrode itself disposed to be separated from and to confront the substrate and not suspended in a gas. This is advantageous, especially in the case where a substrate has a special dimension or size.
  • a substrate 10 is grounded via a conductor 9 and is introduced into the coating apparatus through an entrance 183 by means of a conveyor device 90.
  • a coated substrate leaves the apparatus through an exit 184.
  • the floor 20 of the powder coating apparatus of this invention has an inner surface part which is composed of a face-silent discharge electrode 2.
  • a high AC voltage from a power source 6 is impressed between every two adjacent electrode bars 1 of the electrode and the whole electrode is connected to a DC power source 7 and a conductor 8 to apply a DC potential against the grounded substrate.
  • the inner surface of a side wall of the entrance 183 is composed of a face-silent discharge electrode 174 which generates a travelling wave alternating electric field which proceeeds downwardly.
  • the inner surface part of the side wall of exit 184 is composed of a face-silent discharge electrode 177 which generates a travelling wave alternating electric field which proceeds downwardly.
  • a ceiling 179 and a side wall 181 is impressed by means of a power source 180, a weak alternating voltage which is sufficient for preventing adherence of powder particles, but not sufficient for generating a silent discharge.
  • a power source 7-3 feeds the electrode 174 as well as the electrode 177 with a three-phase alternating electric field.
  • a powdery coating material 11 stored in a hopper is fed from an opening 172 of a chute via a powder feeder 12 directly to the face-silent discharge electrode 2 which constitute the floor of the apparatus.
  • Reference numeral 1 denotes electrode bars in the inner surface part of the face-silent discharge electrode of the floor.
  • Face-silent discharge electrodes of three-phase type capable of generating travelling wave alternating electric fields which proceed downwardly are employed in the inner surface parts of side walls to prevent suspended coating material powder from travelling upwardly along the side walls.
  • the face-silent discharge electrodes disposed in the side walls of the apparatus generate a travelling wave alternating electric field which drives the powder particles downwardly.
  • inner surfaces of articles having depressions such as bottles, bombs and caps, can be easily powder coated at a high speed to form an excellent coating, with an apparatus of small size.
  • a suitable apparatus therefor will be described in the following.
  • FIG. 17a is a side view, partially showing sections, of a powder coating apparatus of this invention where an inner surface of a substrate 10 having a bomb-like shape is being coated.
  • FIG. 17b is a horizontal cross section of a part of said apparatus.
  • a coating material powder 11 stored in a hopper is fed to a ring fluidizing chamber 77 via powder coating material feeder 12.
  • a ring gas feeding chamber 76 Under the fluidizing chamber 77 is installed a ring gas feeding chamber 76. Chamber 77 is separated from chamber 76 by a perforated plate 79.
  • a gas is injected into the gas feeding chamber 76 by a fan 99 as shown by arrow 114 and through a valve 97.
  • the coating material powder 81 which has been fluidized by the injected gas fed from the blowing chamber 76 in the fluidizing chamber 77, gushes forth upwardly in a suspended state through a plurality of holes 80 arranged in the ceiling of chamber 77.
  • a face-silent discharge electrode 2 of stick shape is installed in the central part of the apparatus. In the outer surface part of the stick, are arranged electrode bars 1-1 and 1-2 of spiral form so as to generate a silent discharge over the entire outer surface of the stick.
  • the stick is hollow and is provided with a small hole at the bottom from which the gas is exhausted to be excluded as shown by arrow 113.
  • a substrate 10 is positioned over the face-silent discharge electrode of stick shape so that the inner surface of the substrate and the outer surface of the electrode are in concentric relation.
  • Valve 97 is opened and suspended powder coating material is allowed to gush forth into the coating space 18 between the inner surface of the substrate and the face-silent discharge electrode.
  • powder coating material which is carried by the blown gas from blowing chamber 76 rises in the space 18.
  • the gas flows into the inside 116 of the face-silent discharge electrode via a small top hole 112 to be exhausted as shown by arrow 113.
  • An AC voltage is impressed between two adjacent electrode bars by a power source 6 and a DC voltage is impressed between the face-silent discharge electrode and the substrate 9 by means of a power source 7 and a conductor 8.
  • the coating of the inner surface of a separate body is thus completed while completely preventing the fly losses due to over spray. Accordingly, the inner surface of a separate substrate 10 is coated without any special recovering installation by employing the substrate itself as a recovering device in accordance with this invention. An excellent coating on the inner surface is easily obtained at a high speed with an apparatus of small size. The procedure can be practiced even when the apparatus, the longitudinal sectional view thereof is shown in FIG. 17a, does not have a concentric relationship with the substrate as shown in FIG. 17b.
  • the apparatus of this invention can be employed for powder coating the inner surface of an elongated article having U-shaped section. One example of such apparatus is illustrated by FIG. 17c which is an oblique view thereof.
  • both the inner surface and the outer surface of a substrate 10 can be concurrently powder coating to form powder layers.
  • the procedure is exemplified in FIG. 17d on which a face-silent discharge electrode 2 is arranged to confront both the inner surface and the outer surface of a hollow cylindrical substrate 10.
  • Other structures are the same as in FIG. 17a.
  • the construction of the face-silent electrodes should be selected so as to generate safely and surely a silent discharge.
  • a suitable field strength and a suitable current density at the surface of the substrate should be selected, depending upon the properties of coating material used.
  • the feed rate of the powder and the coating time should be selected to be suited to the conditions mentioned above.
  • the substrate is a steel pipe for piping having an inner diameter of 16 mm and a length of 5.5 mm.
  • the inner surface of said pipe is to be coated with an epoxy resin powder coating material.
  • a face-silent discharge electrode of 3 mm in outer diameter and 5 mm in length is coaxially disposed in the steel pipe to be coated.
  • the face-silent discharge electrode is suspended at the lower end of a pipe for powder feeding.
  • the face-silent discharge electrode fixed to the pipe for powder feeding is suspended into the upright steel pipe.
  • An epoxy resin coating material powder is fed at a rate of about 45 g per minute through the pipe for powder feeding.
  • the face-silent discharge electrode is made of a vitreous insulator. Two conductor electrode bars of 0.3 mm in breadth are embedded in parallel at a depth of 0.3 mm. Embedded electrode bars form two parallel spirals having a pitch of 6 mm. An AC voltage of 4.5 KV, 50 Hz is impressed between two electrode bars. The potential of the face-silent discharge electrode is maintained at 5.5 KV against the grounded substrate of steel pipe. The coating is performed while maintaining the relative speed between the face-silent discharge electrode and the substrate of pipe at 5 cm/sec. After baking, a uniformly thick coating of 200 ⁇ in mean thickness with a standard deviation of ⁇ 10 ⁇ is obtained. Ten pieces of coated pipe were examined and no pinholes found. The coating efficiency attains to 95% in this case.
  • the substrate coil is of 30 cm in breadth.
  • the speed of the substrate is of 20 cm per minute.
  • the insulator of the electrode is of an epoxy resin which have been modified to have a low volume resistivity.
  • the shape of the face-silent discharge electrode 2 employed is as shown in FIG. 6.
  • the electrode bars and the face electrode are embedded in the insulator of said epoxy resin.
  • the breadth of electrode bar is of 0.5 mm and the spacing thereof is of 5 mm.
  • a face-silent discharge electrode where the spacing between the face electrode and the plane including electrode bars is of 1 mm is employed.
  • An AC voltage of 4000 V, 50 Hz is impressed between the electrode bars and the face electrode.
  • the spacing between the face-silent discharge electrode 2 and the substrate 19 is maintained at a value of 10 cm.
  • the length of the face-silent discharge electrode in the direction of proceeding of the substrate is of 70 cm and the breadth is of 36 cm.
  • the potential of the face-silent discharge electrode is maintained at a value of -30 KV against the grounded substrate.
  • a polyester coating material powder stored in a hopper is fed through a feeder at a rate of 1300 g per minute.
  • the air for powder feeding, shown by arrow 75 in FIG. 15, is fed at a rate of 2.7 m 3 per minute.
  • a uniformly thick coating is continuously formed on the substrate. After baking, a coating of 250 ⁇ in thickness with standard deviation of ⁇ 15 ⁇ is obtained and no pinholes found.

Landscapes

  • Electrostatic Spraying Apparatus (AREA)
  • Application Of Or Painting With Fluid Materials (AREA)
US05/593,722 1974-07-10 1975-07-07 Electric discharge coating apparatus Expired - Lifetime US3976031A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP49078226A JPS60108B2 (ja) 1974-07-10 1974-07-10 放電塗装装置
JA49-078226 1974-07-10

Publications (1)

Publication Number Publication Date
US3976031A true US3976031A (en) 1976-08-24

Family

ID=13656122

Family Applications (1)

Application Number Title Priority Date Filing Date
US05/593,722 Expired - Lifetime US3976031A (en) 1974-07-10 1975-07-07 Electric discharge coating apparatus

Country Status (4)

Country Link
US (1) US3976031A (en, 2012)
JP (1) JPS60108B2 (en, 2012)
CH (1) CH593718A5 (en, 2012)
GB (1) GB1509389A (en, 2012)

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4011991A (en) * 1974-08-04 1977-03-15 Senichi Masuda Electrostatic powder painting apparatus
FR2343514A1 (fr) * 1976-03-08 1977-10-07 Onoda Cement Co Ltd Appareil a rideau de champ electrique du type de securite
FR2370526A1 (fr) * 1976-11-10 1978-06-09 Onoda Cement Co Ltd Procede continu de revetement electrostatique avec une matiere pulverisee, et appareil utilise pour mettre en oeuvre ce procede
FR2370525A1 (fr) * 1976-11-10 1978-06-09 Onoda Cement Co Ltd Procede et appareil pour appliquer electrostatiquement des revetements de poudre
US4170194A (en) * 1976-11-15 1979-10-09 Etlin Vladimir N Apparatus for electrostatic deposition
US4230068A (en) * 1977-06-13 1980-10-28 Onoda Cement Company, Ltd. Apparatus used in continuous process for electrostatic coating with pulverized material
WO1980002236A1 (en) * 1979-04-19 1980-10-30 V Etlin Means and method for electrostatically applying powder coating to an article
US4233335A (en) * 1979-03-06 1980-11-11 Etlin Vladimir N Electrostatic coating method
US4321281A (en) * 1976-11-10 1982-03-23 Onoda Cement Co., Ltd. Process for electrostatic coating with pulverized material and apparatus used in said process
US4324198A (en) * 1979-09-12 1982-04-13 Weitman And Konrad Gmbh & Co. Kg Device for the electrostatic application of material particles entrained in a stream of gas to an advancing, flat substrate
US4563977A (en) * 1983-08-29 1986-01-14 Walter Spengler Electrostatic coating plant
US4749593A (en) * 1985-02-21 1988-06-07 Prazisions-Werkzeuge Ag Coating arrangement and process for preventing deposits of a coating material
US4915978A (en) * 1986-08-27 1990-04-10 Nukem Gmbh Method and device for forming a layer by plasma-chemical process
US5540772A (en) * 1988-12-27 1996-07-30 Symetrix Corporation Misted deposition apparatus for fabricating an integrated circuit
US5749973A (en) * 1987-06-08 1998-05-12 Canon Kabushiki Kaisha Apparatus for spraying particulate material in an evaporatable dispersion having elecrical potential
US20030159654A1 (en) * 2002-01-23 2003-08-28 Gregor Arnold Apparatus for plasma treatment of dielectric bodies
US6890475B1 (en) * 1998-05-15 2005-05-10 Oy Oms Optomedical Systems Ltd. Method and apparatus for manufacturing a thin-walled article
WO2005056197A1 (en) * 2003-12-10 2005-06-23 Kinesis S.R.L. A device for powder painting, and a painting process that uses said device
US20050281957A1 (en) * 2004-06-21 2005-12-22 Mystic Tan, Inc. Misting apparatus for electrostatic application of coating materials to body surfaces
US7374331B1 (en) 2005-02-18 2008-05-20 Goodson David M Method and apparatus electrostatically controlling the viscosity and other properties of ceramic compositions
US20090145743A1 (en) * 2005-03-16 2009-06-11 Gennady Yumshtyk Sputtering devices and methods
EP2837459A1 (en) 2013-08-17 2015-02-18 Somont GmbH Systems and methods for applying particles in a gas flow to a workpiece
US20160015843A1 (en) * 2014-07-16 2016-01-21 Lg Electronics Inc. Plasma device and an air conditioner including a plasma device
US9368330B2 (en) 2014-05-02 2016-06-14 Bh5773 Ltd Sputtering targets and methods
EP3034173A1 (de) * 2014-12-17 2016-06-22 Eisenmann SE Vorrichtung und verfahren zum abscheiden von partikeln aus einem abluftstrom einer beschichtungskabine
US9646806B2 (en) 2014-03-25 2017-05-09 Lg Electronics Inc. Plasma electrode device and method for manufacturing the same

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS58171252U (ja) * 1982-05-10 1983-11-15 トヨタ車体株式会社 静電装置

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3098150A (en) * 1960-06-13 1963-07-16 Inoue Kiyoshi Spark discharge metal depositing apparatus
US3318790A (en) * 1964-04-29 1967-05-09 Texas Instruments Inc Production of thin organic polymer by screened glow discharge
US3600218A (en) * 1968-05-15 1971-08-17 Ibm Method for depositing insulating films of silicon nitride and aluminum nitride
US3677799A (en) * 1970-11-10 1972-07-18 Celanese Corp Vapor phase boron deposition by pulse discharge
US3798048A (en) * 1971-07-27 1974-03-19 Nyvel Corp Method and apparatus for electrostatically coating an object
US3865079A (en) * 1973-08-27 1975-02-11 Gen Motors Corp Electrostatic fluid bed powder coating system
US3874333A (en) * 1972-09-28 1975-04-01 Nat Steel Corp Preventing edge wrap-around in one-side electrostatic coating

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3098150A (en) * 1960-06-13 1963-07-16 Inoue Kiyoshi Spark discharge metal depositing apparatus
US3318790A (en) * 1964-04-29 1967-05-09 Texas Instruments Inc Production of thin organic polymer by screened glow discharge
US3600218A (en) * 1968-05-15 1971-08-17 Ibm Method for depositing insulating films of silicon nitride and aluminum nitride
US3677799A (en) * 1970-11-10 1972-07-18 Celanese Corp Vapor phase boron deposition by pulse discharge
US3798048A (en) * 1971-07-27 1974-03-19 Nyvel Corp Method and apparatus for electrostatically coating an object
US3874333A (en) * 1972-09-28 1975-04-01 Nat Steel Corp Preventing edge wrap-around in one-side electrostatic coating
US3865079A (en) * 1973-08-27 1975-02-11 Gen Motors Corp Electrostatic fluid bed powder coating system

Cited By (31)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4011991A (en) * 1974-08-04 1977-03-15 Senichi Masuda Electrostatic powder painting apparatus
FR2343514A1 (fr) * 1976-03-08 1977-10-07 Onoda Cement Co Ltd Appareil a rideau de champ electrique du type de securite
US4377603A (en) * 1976-11-10 1983-03-22 Onoda Cement Company, Limited Method and apparatus for electrostatic powder coating
FR2370526A1 (fr) * 1976-11-10 1978-06-09 Onoda Cement Co Ltd Procede continu de revetement electrostatique avec une matiere pulverisee, et appareil utilise pour mettre en oeuvre ce procede
FR2370525A1 (fr) * 1976-11-10 1978-06-09 Onoda Cement Co Ltd Procede et appareil pour appliquer electrostatiquement des revetements de poudre
US4321281A (en) * 1976-11-10 1982-03-23 Onoda Cement Co., Ltd. Process for electrostatic coating with pulverized material and apparatus used in said process
US4170194A (en) * 1976-11-15 1979-10-09 Etlin Vladimir N Apparatus for electrostatic deposition
US4230068A (en) * 1977-06-13 1980-10-28 Onoda Cement Company, Ltd. Apparatus used in continuous process for electrostatic coating with pulverized material
US4233335A (en) * 1979-03-06 1980-11-11 Etlin Vladimir N Electrostatic coating method
WO1980002236A1 (en) * 1979-04-19 1980-10-30 V Etlin Means and method for electrostatically applying powder coating to an article
US4324198A (en) * 1979-09-12 1982-04-13 Weitman And Konrad Gmbh & Co. Kg Device for the electrostatic application of material particles entrained in a stream of gas to an advancing, flat substrate
US4563977A (en) * 1983-08-29 1986-01-14 Walter Spengler Electrostatic coating plant
US4749593A (en) * 1985-02-21 1988-06-07 Prazisions-Werkzeuge Ag Coating arrangement and process for preventing deposits of a coating material
US4915978A (en) * 1986-08-27 1990-04-10 Nukem Gmbh Method and device for forming a layer by plasma-chemical process
US5749973A (en) * 1987-06-08 1998-05-12 Canon Kabushiki Kaisha Apparatus for spraying particulate material in an evaporatable dispersion having elecrical potential
US5540772A (en) * 1988-12-27 1996-07-30 Symetrix Corporation Misted deposition apparatus for fabricating an integrated circuit
US6890475B1 (en) * 1998-05-15 2005-05-10 Oy Oms Optomedical Systems Ltd. Method and apparatus for manufacturing a thin-walled article
US20030159654A1 (en) * 2002-01-23 2003-08-28 Gregor Arnold Apparatus for plasma treatment of dielectric bodies
WO2005056197A1 (en) * 2003-12-10 2005-06-23 Kinesis S.R.L. A device for powder painting, and a painting process that uses said device
US20050281957A1 (en) * 2004-06-21 2005-12-22 Mystic Tan, Inc. Misting apparatus for electrostatic application of coating materials to body surfaces
US7462242B2 (en) * 2004-06-21 2008-12-09 Mystic Tan, Inc. Misting apparatus for electrostatic application of coating materials to body surfaces
US7374331B1 (en) 2005-02-18 2008-05-20 Goodson David M Method and apparatus electrostatically controlling the viscosity and other properties of ceramic compositions
US20090145743A1 (en) * 2005-03-16 2009-06-11 Gennady Yumshtyk Sputtering devices and methods
US8741115B2 (en) * 2005-03-16 2014-06-03 Bh5773 Ltd Sputtering devices and methods
US9583319B2 (en) 2005-03-16 2017-02-28 Bh5773 Ltd Sputtering devices and methods
EP2837459A1 (en) 2013-08-17 2015-02-18 Somont GmbH Systems and methods for applying particles in a gas flow to a workpiece
WO2015025234A1 (en) 2013-08-17 2015-02-26 Somont Gmbh Systems and methods for applying particles in a gas flow to a workpiece
US9646806B2 (en) 2014-03-25 2017-05-09 Lg Electronics Inc. Plasma electrode device and method for manufacturing the same
US9368330B2 (en) 2014-05-02 2016-06-14 Bh5773 Ltd Sputtering targets and methods
US20160015843A1 (en) * 2014-07-16 2016-01-21 Lg Electronics Inc. Plasma device and an air conditioner including a plasma device
EP3034173A1 (de) * 2014-12-17 2016-06-22 Eisenmann SE Vorrichtung und verfahren zum abscheiden von partikeln aus einem abluftstrom einer beschichtungskabine

Also Published As

Publication number Publication date
JPS60108B2 (ja) 1985-01-05
JPS518347A (en, 2012) 1976-01-23
GB1509389A (en) 1978-05-04
CH593718A5 (en, 2012) 1977-12-15

Similar Documents

Publication Publication Date Title
US3976031A (en) Electric discharge coating apparatus
US4086872A (en) Electrostatic coating with post charger web or coil coating and powder feed
FI64059B (fi) Foerfarande och anordning foer kontinuerlig elektrogasdynamiskbelaeggning av en serie arbetsstycken
US5279863A (en) Electrostatic powder coating apparatus and method
US3336903A (en) Electrostatic coating apparatus
US4219864A (en) Device and method for moistening and/or discharging electrically insulating objects and materials
MXPA97002463A (en) Apparatus for covering substrates with inductivame loaded powder resin particles
US4084019A (en) Electrostatic coating grid and method
US3566833A (en) Continuous coating apparatus
US3155545A (en) Apparatus for external coating of objects
US3673463A (en) Methods and apparatus for electrogasdynamic coating
US4427712A (en) Electrodynamic coating process
US3376156A (en) Spray painting employing high voltage charging
JPH0636892B2 (ja) 渦流効果静電流動化ベツド被覆着け方法及び装置
US4780331A (en) Method and apparatus for induction charging of powder by contact electrification
GB1588503A (en) Installation and method for electrostatic powder coating of articles
JPS5945425B2 (ja) 粉体塗装装置
US3016876A (en) Apparatus for electrostatically spray coating articles
GB2145641A (en) Apparatus for electrostatically coating articles
CA1065128A (en) Method of and apparatus for coating objects with powdered or granular particles, flakes or fibres
US4808432A (en) Electrostatic coating apparatus and method
US3891415A (en) Electrostatic dust collector for exhaust gases containing fine particles
US4795339A (en) Method and apparatus for depositing nonconductive material onto conductive filaments
US7261764B1 (en) System and method for spatially-selective particulate deposition and enhanced deposition efficiency
US4772982A (en) Powder charging apparatus and electrostatic powder coating apparatus